Telephone-exchange system



Feb. 26 1924.

. 1,485,005 J. 1.. WRIGHT TELEPHONE EXCHANGE S Y STEM Filed Aug. 12 1916 5 Sheets-Sheet 1 Feb. 26, 1924. a v 1,485,005

J. L. WRIGHT TELEPHONE EXCHANGE SYSTEM Feb. 26, 1924 1,485,005

J. L. WRIGHT TELEPHONE EXCHANGE sYsTEM Filed Aug. 12, 1916 ANOTHER TRUNK J.lm VVRIGHiT TELEPHONE EXCHANGE SYSTEM Feb. 26, 1924. v 1,485,005

Filed Aug. 12 19 6 5 Sheets-Sheet 4 lff u Feb. 26 1924.

J. L. WRIGHT TELEPHONE EXCHANGE SYSTEM Filed Aug. 12, 1916 5 Sheets-Sheet 5 reamed Feb. as, less.

JOSEPH L. WRIGHT, or CLEVELAND, OHIO, ASSIGNOR ro WESTERN ELECTRIC colu- PA Y, rncoaroaarnn, or NEW YORK, .11. 3., a oon-Pom'rron- TELEPHONE-EXCHANGE SYSTEIvi.

Application filed August 12,1916. Serial 110. 114,516.

To aZZ whom it may concern:

Be it known that I, Josnrrr L. WRIGHT, a citizen of the United States, residing at Cleveland, in the county of Cuyahoga and State of Ohio, have invented certain new andnseful Improvements in Telephone-EX- change Systems, of which the following is a specification.

My invention relates to telephone exchange systems, and especially tov systems employing operators in I conjunction with automatic apparatus.

The object of my invention is to produce a system which is rapid in operation and re quiring but a minimum number of acts on part of the operator atthe central otlice to receive and establish connections.

My invention embraces such features as automatically associating a calling line with an idle operators cord circuit or trunk, to automatically connect the operators telephone set to the calling line and at the same time render the operators position busy against other calls until the connection is established. In establishing connections the only duty performed by the operator is, that of placing the plug associated with the trunk or cord into the jack of the called subscribers line. The testing, ringing. and automatic disconnection of the calling and called subscribers lines is performed automatically without any attention on part of the operator.

The calling lines are automatically connected to idle trunks or cord circuits by means of what are termed tens and units relays. These relays are formed into groups and operated in order to establish connections in the manner similar to corresponding relays of the following. Clementpatents: 1,105,490 of July 28, 1914; 939,188 of November 2, 1909; 1,1011% of August 11, 1914 and 1,107,152 of August 11, 1914.

In the present instance provision is made to prevent interference in case of simultaneous calls in the same or different groups of tens and units relays. Provision is also made for enabling a large number of what are termed primary trunks to be rapidly distributed among a large number of what are termed secondary trunks. These secondary trunks terminate in cord circuits located at the various operators positions.

Other features of my invention will be pointed out in the detail description to follow. i

My invention is illustrated in the accompanying drawings, wherein:

'Figure 1 shows a plurality of subscribers linefequipments at the central otfice with a set of control relays for regulating the action of the tens and units relays.

Figure 2 shows a primary trunk with its associated tens and units relays.

Figure 3 shows the circuits and relays for controlling the tens and units relays associated with the secondary trunks.

Figure 4 shows a portion of a secondary trunk with means for controlling individual groups or sets of trunks.

Figure 5 shows a secondary trunkvterminating on a cord circuit at the operators position. i

Referring to Figures land 2, relay, 203 represents a tens relay asssociated with the primary trunk, while relay 204 represents one of the units relays associated with this trunk. In practice, and as disclosed in the Clement patents mentioned, there Will be a bank or group of these relays associated with each primary trunk. Each tens reIay will preferably contain contacts. associated with ten subscribers lines. In caseten relays are provided then each primary trunk is capable of serving one-hundred subscribers lines. Each trunk in thiscase will also be provided with ten unitsrelays in order to form the proper cross combinations with the tens relays. I

Figure 1 shows the line and cut-ofi' relays associated with six subscribers lines numbelecl 11, 12, 13, 21, 22 and 23. A set of relays numbered 1A to 10-A, of which in the present instance only. three are shown, serve to control the action of the tens relays associated with the primary. trunks. A similar group of relays numbered 1-B to 10B of which onlythree are shown, serve to control the action of the units relays associated with the primary trunks.

Associated with each of the relays 1-lX to 10-A is a master relay such as 101 which serves to connect the units wires in a group of ten line relays so as to enable one or more relays of the group 1-B to 10B to be operated as the case may be. As the conl if its

tacts associated with relays 1-A. to 10-A for controlling the master relays are in series relation it, of course, follows that the operation'ol but one or these relays is effected. The series contacts are guarded by the portion 111 of the switch X. This switch X is a stepby-step switch provided with three sets of wipers and bank contacts designated as 111, 112 and 113. This switch is caused to step once at each call originated and also in case abnormal condition is created.

As only one master relay such as 101 is capable of being operated at the same instant it follows that calls can be originated at the same instant from a particular group I of ten lines whose connections are controlled by the operated relay 101. The operation of relay 101 serves to control the operation J or" the tens relay associated with the primary trunk. 7 Each master relay as 101 controls an individual tens relay of the group. Relay 102 is operated by any relay in the group 1--A to 10A and serves when so operated to sever the tens starting wires to prevent further operation of relays 1J.i. to 10A. The contacts of relays 1l3 to 10 -3 which control the operation of the units relays of the primary trunks are also in series relation so that but one units relay of a group can be operated at the same time. These series contacts are guarded by means of the portion 112 of the switch X.

In case one of the series wires or contacts are broken preventing the connection from being established from the calling line to the primary trunk the switch will automatically step thereby shifting the ground connections directly to contacts on relays of the sets 1 2; to 10-i-= and 1B to 10B. During this shifting relay 109 will be operated to restore the control relays formerly operated.

The portion 118 of the switch X controls the starting wires to the various primary trunks. When, however, connection is es tablished the starting wire is shifted to the next trunk in the series in order to provide for uniform use of these trunks.

The starting conductor as shown in Figure 2 extends in series through the contacts of relays 206 and 202 or" each primary trunk. A tap or connection is made to each primary trunk through the contacts or" the portion 113 of the switch X. With this arrangement each primary trunk has an individual starting circuit extending from a particular contact on the switch X. This series arrangement is the same as that of the series contacts or" the sets of relays 1A to 10-A and l-B to 10B. When the switch, as shown in Figure 1, is resting on the first contact and should relays 10-A. and 10B be operated then the circuits controlled by their series contact would extend through resacoa the contacts of all the lower relays in the series. This arrangement of wiring is made in order to guard against always starting from a certain'point 1n the ser1es.

Referring to Figure 3, a set of control renumber or" these relays will preferably be allotted to each secondary trunk.

The starting wires leading from the portion 3 14 01" the switch Y of Figure 3 instead oi leading directly to the control relays such as 403, one of which is associated with each secondary trunk are connected in multiple to cont-acts of a set of relays such as 401. Each relay of this set has starting conductors associated with aparticular set of secondary trunks. The starting conductors are in series relation. in other words when one trunk oi a group is busy a relay associated with that trunk serves to shift the starting Wire to the neXt trunk in the series.

In case all of the trunks of a group controlled byrelay 401 are busy then the switch Z will step to the next contact and thereby cause the operation of a relay as 401 associated with the next group of secondary trunks. 7

"With the foregoing arrangement it is possible to allow the interconnection of a large number of primary trunks with an equally large number of secondary trunks.

Referring to. Figure 5, the secondary trunk is shown terminating in a plug P. This plug is connected to a flexible con ducting cordott the usual type. Condensers 49 and 59 are inserted in the talking conductors or the cord circuit in the usual manner. Relay 501 provided with two windings serves to supply talking current to the calling subscriber while talking current is supplied to the called subscriber through the winding of relay 504 and the winding of the retardation coil 505. V Relay 500 is automatically operated upon the origination of a call and serves to con meet the operators telephone set to the trunk while lamp 512 is also lighted at the same time thus indicating to the operator upon which trunk or cord circuit the call is connected. Relays 502 and 509 are slow acting relays, the former serving to prevent accidental disconnection of the calling subscribers line in case he should inadvertently operate his switch hook. Relay 510 operated in- 'conjunction with thezresistancecoil 129 serves to 'controllthe actionof the cutoff relay of thecalled line. When the plug is placed in the jack J such as shownin Figure 1, relay 510is placed in series with thecut-ofl relay ofthe line associated with the jack. When-the windings of relay510 and the cut-off relay alone are placed in series they will both operate, but when the resistance coil129 is inserted in series'with the windings of these relays then relay5l0 alone will remain operated andthe cut-off relay will restore.

Associated with the cord circuit is a ringing switch R for automatically supplying ringing current to the line of the called subscriber. Each cord circuit is provided with a four-party ringing key K of the usual locking and indicating type. Each key is provided with master springs 517 whichare only operated when any one of the four buttons of the set is in its fully depressed position.

The operation of the system for a local call is as follows:

Subscriber No. 11 upon removing his receiver energizes the line relay associated with his line. The operation of this relay completes the circuit of relay 1A by the following path: ground, contacts of line relay, 16, contacts of relay 102, 17 winding of relay 1A, 24,-to battery B through the contacts of relay 109. The operation of relay 1A completes'the circuit of relay 102 and thereuponthe initial energizing circuit for relay 1A is broken. The circuit of this relay is, however, maintained locked to ground over conductor 16.

The operation of relay 1 A also co-mpletes the circuit of relay 101 by the follow- 111g path: ground, portion 111 of the-switch X, '19, contacts ofrel-ay 1A, 20, winding of relay 101, to battery B. The operation of this latter relay allows the circuit of relay 1B to be completedby the following path: ground, contacts of the line relay,l2l, contacts of relay 101, 22, contacts of relay 108, 23, winding of relay 1-B, 24, to battery B through the contacts of relay 109. The operation of relay 1-B completes the circuit of relay 103, which in operating opens the initial energizing circuit for relay 1B which is thereafter maintained locked to ground over conductor 22.

The circuit of the control relay 200 of an idle primary trunk is completed as follows: ground, contacts of relay 1B, 40, contacts of relay 500, 41, portion 113, of the-switch X, 42, contacts of relay 206, '43, winding of relay 200, to battery B. The operation of relay 200 allows the circuit of the tens relay 203 to be completed by the following path: ground, contacts of relay 101, 34, contacts of relay 200, 35, winding of relayv 203, to battery B. The operation of relay 200 also allows the circuit of the units relay 204 to be completed byLthe followingpath: ground, portion'112 of the switch X, 27 contacts-of relay .1B, 28, contacts of relay 200, v29, winding of relay .204, to battery B. The operation of'relays 203 and 204 places relay 206 in series with the winding of the cut-off relay associated'with subscriber sline No. 11 by the following path: battery 13, winding of relay 206, 66, contacts of relay 204, 65, contacts of relay 203, 64, winding of the cutofi relay to ground.

The operation of the cut-on relay disconnects and causes therestoration of the line relay associated with subscribefsline No. 11. The restoration of this relay removes ground from the locking contacts of relays 1A;and 1 l3. The restoration of relay l+A releases relay 102 and also relay 101. The restoration of relay 1B releases relay 103 and also relay 200 (Figure 2).

The operation of relay 206 also serves to disconnect relay 200.

While relay 200 is energized it completes the circuit of relay 202 which disconnects the starting wire 74 leading to the next trunk of the series, thus preventing any possible interference with therelays 'oftliat trunk.

The operation of relay 200 also completes the circuit of relay 201 which thereafter has its circuit completed or maintained through its locking contact-to ground and to battery B through the contacts of relay 205.

The operation of relay 206 when placed in series with the cut-off relay of the calling line disconnects the starting'wire from relay 200 and continues it to the nexttrunk of the series.

The circuits of relays 203 and 204 are both maintained locked to ground through the contacts of relay 201. Relay 204 has a resistance coil 31 included in its locking circuit whilerelay 203 has a similar coil 37 included in its locking circuit.

As soon as an idle primary trunk is selected and placed in association with the calling line in the manner just described a secondary selection is next made in order to connect the primary trunk to an idle secondary trunk or cord circuit.

This selection is made in the following manner: The operation of relay 206 completes the circuit of relay 300 by the following path: ground, contacts of relay 201, 70, contacts of relay 206, 71, winding of relay 300 to battery B. The operation of re lay 300 completes the circuit of relay V1C by the following path: ground,contacts of relay 300, 82, contacts of relay 308, 83, winding of relay '1C to battery B through the contacts'of relay 304. The operation of relay 1C completes the circuit of relay 308. After the operation of relay 308 the circuit of relay 1@ is maintained locked to ground over conductor 82. The operation of relay 1-C also completes the circuit of relay 307 by the following path: ground, portion 313 of the switch Y, 96, contacts of relay 1C, 97, winding of relay 307 to bat tery B. .The operation of relay 307 allows the circuit of relay 1-D to be completed by the following path: ground, contacts of relay 300, 78, contacts of relay 307, 79, contacts of relay 310, 80 winding of-relay lD, 81, to battery B through the contacts of relay 304. The operation of relay lD completes the circuit of relay 310 which opens the initial energizing circuit of relay lD,

which thereafter has its circuit maintained locked to ground over conductor 79.

The operation of relay lD also conr pletes the circuit of relay 401 of a group of idle secondary trunks by the following path: ground, contacts of relay lD, 98, portion 409 of the switch Z, 99, winding of relay 401 to battery B. The operation of relay 401 allows the circuit of relay 403 associated with an idle secondary trunk to be completed by the following path: ground, contacts of relay 1-D, 104, winding of relay 309, 105, portion 314 of the switch Y, 106, contacts of relay 401, 107, contacts of relay 408, 108, contacts of relay 402, 109, contacts of relay 400, 110, winding of relay 403 to battery V The operation of relay 403 allows the circuit of the tens relay 404 to be completed by the following path: ground, contacts of.

relay 307 (Figure 3), 85, contacts of relay 403, 95, winding of relay 404 to battery B. The operation of relay 403 also allows the circuit of the units relay 405 to be completed by the following path: ground, contacts of relay 309, 86, coil 87, 88, portion 312 of the switch Y, 89, contacts of relay -1D, 90, contacts of rela 403,91 windin Y 7 z) of relay 405, to battery B.

The operation of relays 405 and 404 connects the primary trunk to the secondary trunk whereupon relay 402 (Figure 4) is placed in series with relay 205 by the following path: battery B, winding of relay 402, 78, 77, contacts of relay 405, 76, contacts of relay 404, 7 5, winding of relay 205, to ground.

Relay 405 after being energized has its circuit maintained to ground by the following path: battery B, winding of relay 405,

contacts of relay 405, coil 92, 93, contacts of relay 402, 112 to ground through. the contacts of relay 509 (Figure 5). Relay 404 after being energized has its circuit maintained locked by the following path: battery B, winding of relay 404, contacts of relay 404, 94, winding of relay 406, 93, contacts of relay 402, 112 to ground through the contacts of relay 509. The operation of relay 402 which maintains the circuits of relays 405 and 404 energized in the manner just described also shifts the starting conductor 107 to the next trunk in the series or group.

Relay 409 was energized at the first opera 7 tion of relay 403 and serves to, sever the starting circuit leading to the next trunk the series or group to prevent interference.

The operation of relay 205' (Figure 2) removes battery from the winding of relay 201 thereby causing its restoration. The

restoration of this relay removes ground from the winding of relay 300 (Figure 3) which upon restoring .releases relays lC and lD. The releasing of relay 1C causes the restoration of relay 308 and also the restoration-of relay 307. The restora: tion of relay 1-'D causes the restoration of relay 310 and also relays 309, 401 and 403.

The operation of relay 402 and relay 406.

completes the circuit of relay 500 (Figure 5) by the following path: ground, contacts of relay 509, 112, contacts of relay 402, 113, contacts of relay 406, 114, winding of relay 500,

115, contacts of relay 510, 116 to battery B through the contacts of relay 508. V

The operation of relay 500 connects the operators telephone set directly across the tip and sleeve conductors 48 and 58 allowing her to converse w1th the calling subscriber.

The lamp 512 has its circuit completed in tacts of relay 510,115, contacts of relay 500,

117, contacts of relay 408, to ground. The operation of relay 408 which is common to the particular operators position upon which a call is received, serves to shift the starting wire from all of the cord circuits associated with that position to prevent other calls being received thereon.

Relay 407 is also operated in multiple with relay 408. In case there are twenty-five cords or trunks tov an operators position, relay 408 in operating will render cords 1 to 13 unselectable while relay 407 will. render cords 14 to 25 unselectable.

As soon as the primary trunk is connected to the secondary trunk then battery supply is furnished ,to the calling subscriber through the windings of relay 501 connected to tip and sleeve conductors '48 and 58 respectively. The operation of relay 501 completes the circuit of the slow acting relay 502 but at this time no effect is produced lloy the operation of either of these two reays; I

The operator upon learning the number desired places theplug P into the jack of the called-for line. In making this connection the operator pays no attention to the condi tion of the line. The insertion of the plug places busy test relay 507 and the cut-oil relay of the called line in series. As the busy test relay 507 has its winding connected to the grounded side of battery and as the winding of the cut-oil relay also has its Winding connected to the grounded side of battery no effect is produced in case the line is idle.

The operator disregarding the fact whether the line is busy or idle presses one of the ringing buttons thereby connecting the proper frequency of general or current to the cam sprin 522 of the ringing switch. R. The depressing of the button also closes the master springs 517. The operation of these springs completes the circuit of relay 503 by the following path: battery B, contacts of relay 508, springs 517, 150, contacts oi relay 502, winding of relay 503, 137, resistance coil 136, 135, contacts of relay 509 to ground. The operation of relay 503 closes the tip and sleeve conductors and connects the winding of relay 51.0 in series with the cut oil relay of the called line by the following path: battery B, winding of relay 510, 130, contacts of relay 501, 131, contacts of relay 503, 126, sleeve of the plug P, jack of the called line, winding of cut-off relay to ground. The operation of relay 510 disconnects the winding of relay 507 and also completes the circuit of the stepping magnet 535 of the ringing switch R by the following path: ground, winding of relay 527, contacts of relay 526, 149, winding of magnet 535, 1 17, contacts of relay 510, 146, contacts of relay 503, 145, contacts of relay 509, 144, contacts of relay 506, 138, contacts of relay 50%, 139, contacts of relay 510, 116, contacts of relay 508 to battery B.

Relay 527 and magnet operate in series. The operation of the magnet causes the switch to step while the operation of the relay completes the circuit of relay 520. This latter relay in operating breaks the series circuit between relay 527 and the magnet 525 thereby causing their restora tion. The restoration of relay 52? in turn causes the restoration of relay which upon fully restoring again places the winding of relay 527 in series with the winding of magnet The cooperation of the magnet and relays in this manner causes the switch to stop until its circuit is interrupted. In addition to the energizing circuit oi the magnet 535 as just traced, its circuit is also directly completed to ground through the contacts of relay 52? when it is energized.

The switch R in stepping operates the cams. are, 519, 520, 521, 522, 523, 524 and 525. The cams 519 and 521 operating open the contacts controlled by them. At the same time these contacts are broken cam 522 operates, closes its associated contacts and connects the proper generator current to the tip conductor 52. The operation of cam 523 at the same instant connects ground to the sleeve conductor 62. This ground is supplied through the back contact oi? relay 50 1. During the ringing interval cam 518 operates its associated con tacts thereby connecting a suitable ring baclr signal to conductor 18 in series with the condenser 141.

Immediately after the ringing interval and before the tip and sleeve conductors are closed by the cams 521 and 519 the cam 520 operates to connect battery to the sleeve conductor in series with the coil 511 for removing any static charge on the line. The removel of this static charge prevents any possibility of the relay 504 prematurely operating.

At the first step of the ringing switch It the cam closes its associated contacts and connects battery directly to the windingof the stepping magnet thus insuring a complete rotation of the switch. [is the magnet 535 has its circuit completed by this path the switch will continue to rotate until it reaches its normal position.

The cam 524; serves to prevent the operation of relay 506 in case relay 504 should be operated by any unusual line condition or operation of the telephone by the called subscriber.

When the called subscriber answers during a non-ringing interval relay 504: is operated. The operation of this relay completes the circuit of relay 506 by the following path: battery B, contacts of relay 508, 139, contacts of relay 50st, springs controlled by cam 521, winding of relay 506, 135, to ground through the contacts of relay 509. Ground is also supplied in multiple to the conductor 135 through bontacts of relay 50%. This latter ground connection serves to maintain relay 506 operative in case relay 509 is energized in case the calling subscriber should replace his receiver first. After relay 506 is operated its circuit is maintained locked directly to battery through an associated locking contact. The operation of relay 506 opens the initial energizing circuit of the stepping magnet. 535 to prevent the operation of the switch B after it reaches its normal position.

When the connection was established and relay 510 operated the circuitv of relay 500 was broken thereby disconnecting the operators telephone set.

The restoration of relay 500 opens the circuits of relays 107 and 408 thus allowing other calls. to be received upon the cord circuits associated with this particular operators position.

At the termination of the conversation the calling subscriber replacing his receiver causes the deenergization of relay 501 and consequently the deenergization of relay 502. The restoration of the latter relay allows the relay 402 to battery B. As relays-402 and 205 are in series this direct ground connection serves to shunt and cause the restoration of relay 205. The restoration of relay 205 removes ground from the locking contacts of relays 203 and 204 thereby causing their restoration and disconnects the line of the calling subscriber from the primary trunk. The restoration of relays 203 and 204 breaks the series connection between relays 206 and the cut-0E relay of the calling line. The restoration of relay 206 restores the primary trunkto its normal position.

7 The called subscriber upon replacing his receiver causes the restoration of relay 504. This relay in restoring connects battery directly to the winding of relay 503 by the"fol-.

lowing path: battery B, contacts of relay 508, 139, contacts of relay 504, 138, contacts of relay 506, winding of relay 503. The other terminal of this relay is also connected to battery through its locking contact, therefore, this relay will be shunted and restore. The restoration of relay 503 severs the tip and sleeve conductors and allows theresistance coil 129 to be placed in series with the winding of relay 510. The insertion of this coil'is between the winding of relay 510 and the winding of the cut-off relay of the called line. This new series path is as follows: battery B, winding of relay 510, resistance coil 129, 128, contacts of relay 510, third conductor of the plug P, thimble of the jack J, winding of the cutoff relay to ground. The resistances and adjustments of the relays are such that relay 510 will remain energized, but the cutor relay of the called line will restore and thereby allow the line relay of that line to be replaced and in readiness to be operated in case the subscriber should originate a call, although the plug remains in the jack.

The restoration of relay 504 in addition to causing the foregoing effects also momentarily connects ground to the winding of relay 510 by the following path: ground, contacts of relay 504, contacts of relay 506, normally open contacts of relay 503, normally open contacts of relay 510, coil 129, 130, winding of relay 510 to battery B. The effect of this momentary ground connection assists in causing the restoration of the cut-off relay of the called line as its wind ing is also connected to ground.

receiving the disconnect signal withdraws the plug from the jack .thereby'breaking the circuit of relay510. The restoration of this relay in turn causes the restoration of relay 509 and the cord circuit is in condition to receive other calls.

Relay 509 in restoring also removes ground from the winding of relay 402 caus ing its restoration.

In case'the called subscriber doesnot answer and the calling subscriber should replace his receiver the release of the connection is effected in the following manner:

Relay 501 restoring opens the circuit of relay 502. After the restoration of relay 501 and before the restoration of relay 502 ground is connected to the third .conductor of the plug P by the following path: ground, contacts of relay 504, 119, back contacts of relay 506 (which is not operated under these conditions), 120, contacts of relay 501, 124, contacts of relay 502, 125, 0011- tacts of relay 503, 126, to the third conductor of the plug P. This momentary ground connection serves to shunt the cutoff relay of the called line and the action of relay 509 after the complete restoration of relay 502 opens the circuit of relay 503,

which upon restoring allows the-resistance coil 129 to be included in series with the winding of relay 510 and the winding of the cut-off relay of the called line. 7

From the foregoing description it will be noted that the cutoff relay of the called line is restored by the calling subscriber in case the called subscriber does not answer even though the plug remains in the jaolr. The same effect is produced upon the cut-off relay of the called line in case the called subscriber answers and afterward replaces his receiver.

In case the called-for line is busy when the plug is inserted in the jack, then relay 507 will be operated, due to battery B being supplied through the winding of a relay 510 associated with another cord circuit. The operation of relay 507 under these conditions-completes the circuit of relay 508, the operation of relay 508 connects a suitable busy tone signal to the tip conductor 48 in series with the condenser 141 thus notifying the calling subscriber that the called line is busy.

The operator, of course, is not aware that 508 removes battery from the contacts 517 of-the ringing key thus rendering the action of 'these contacts ineffective. As relay 503 is not operated it, of course, follows that relay 510 is not connected to the third conductor of the. plug and consequently its operation is prevented,

Relay 508, of course,- is provided with a signal lamp 633, thusindicating to the operator that the called line is busy.

The calling subscriber upon receiving the busy tone signal replaces his receiver, causing the restoration of relays-501 and 502. The restoration of these relays completes the-circuit of relay 509'by the following path: battery B, contacts of relay 508, 139, contacts of relay 502, winding ofrelay 509 to ground. The operation of relay 509 completesthe circuit of the disconnect lamp 133 and the operator observing this signal withdraws the plug from the jack, allowing the restoration of relay 507, which upon restoring opens the circuit of relay 508. This latter relay in restoring opens the circuit of relay 509.

The selection of a group of secondary trunks is madein the following manner:

In case all the trunks in a group controlled by a relay 401 (Figure 4) which is operated are busy, it will naturally follow that relay 309 whose-winding is included in series with thestarting' circuit will not be operated in series with some trunk relay such as 403 (Figure 4). In case all of the trunks of a group are busy and relay 309 fails to operate then the circuit of the stepping magnet 414 of the switch willbe completed and cause the switch to step. Relay 410 is operated in multiple with the winding of'relay 401 and completes the circuit of relay 411. The operation of relay 411 completes the circuit of relay 412. The operation of this latter relay allows the circuit of the stepping magnet 414 to be completed by the following path: back contacts of relay 309, 100, contacts of relay 311, 101, contacts of relay 412, 102, contacts of relay 413, 103, winding of magnet 414 to battery B. The operationof the magnet completes the circuit of the vibrating relay 413 which in operating opens the circuit of the magnet itself. The action set up between the magnet 414 and therelay 413 issuch that the switch Z stepsuntil relay 309'is-0perated in series with the winding of some relay such as-403 of an idle secondary: trunk.

Under normal conditions 'relay 309 will operate and" restore before the set of relays 410, 411 and 41.2 fully operate. It will also be noted that while relay 309. is energized it completes the circuit of'a slow acting relay 311' which serves to'open thecircuit extending tothe stepping magnet 414 to prevent its operation.

From the foregoing it will-be noted that the switch Z will not step unless all of the secondary trunks of a particular group are busy whereupon it will step and connect the next set of trunks. This operation will be kept up until a group containing an idle trunk is'reached.

The switch X of Figure 1 is caused to step at each incoming call in the following manner: When any line relay operates it connects ground to the common conductor 25 thereby completing the circuit ofrelay 105 through the back'contacts ofrelay 104. The operation of relay 105 completes the circuit of'relay '104 and'relay 104m 0 crating opens the circuit of relay 105. Re ay 105 restoring in advance of'relay 104' completes the circuit of the stepping magnet 110. This stepping magnet has its circuit closed by ground supplied through the back contacts of relay 105 and thefront contacts of relay 104.

Having thus described my invention what I desire-to secure by'Letters Patent is:

1. In a telephone exchange system, the combination with a plurality of" primary trunks, of a plurality of secondary trunks arranged-in groups for interconnecting with said primary trunks, a switch common to all of the groups of secondary trunks and for determining a particular group of'secondary trunks to be used, a relay individual to each group of secondary trunks, said relay controlled through said switch for determining the individual trunk'to be used in said group for interconnecting with said primary trunks.

2. Ina telephone exchange system, the combination of a plurality of primary trunks, of a plurality ofgroups of second ary trunks for interconnecting with said primary trunks, means common to all of the groups of the secondary trunks-for determining the particular group of secondary trunks to beused, means individual to each group of secondary trunks and controlled through said common meansfor determining a particular secondary trunk in the group for interconnection with said primary trunks.

3. In a telephone exchange system, the combination of a plurality of primary trunks, of'a plurality of groups of secondary trunks for interconnecting with said primary trunks, the individual secondary trunks of each group being in series relation, a switch common to all of the groups of secondarytrunks, means controlled from said primary trunks for operating said switch for determining a particular group of secondary trunks to be used, a relay individual to each group of secondary trunks,

means controlled by said switch for operating a particular one of said relays whereby "trunk 1n the group for interconnecting with said primary trunks. V v

5. In a telephone exchange system, the

combination of a plurality of primary trunks, of a plurality of groups of secondary trunks for interconnecting with said primary trun rs, the individual secondary trunks of each'group being in series relation, a switch common to all the groups of secondary trunks, contacts association with said switch, one of: said contacts being allotted to each group of secondary trunks, means controlled by said primary trunks for operating said switch to determine the particular group of secondary trunks to be used, means controlled over the contact of said switch allotted to the selected group for automatically selecting an idle secondary trunk for interconnection with said primary trunks. V

6. In a telephone exchange system, the combination of a calling and a called subscribers line, a link circuit for interconnecting said lines, a relay associated with the called line, means associated with said link circuit for energizing said relay when connection is efiected between said lines, means controlled by the calling and called subscriber for momentarily shunting said relay.

7. In a telephone exchange system, the combination of a calling and a called subscribers' line, a jack and a relay associated 'with said lines, a plug ending trunk, means for automatically connecting the calling line to said trunk, means associated with said trunk for energizing'the relay of the called line when. the plug of the trunk is placed into the jack of the called line, means controlled over either of said lines for disabling said relay while the plug remains in the jack.

8. In a telephone exchange system, the combination of a calling and a called subscribers line, a jack associated with the called line, a cord circuit provided with a plug adapted to engage said jack, means associated with said cord circuit automatically rendered operable when the plug is placed in the jack for indicating to the calla circuit.

ing subscriber in case the called lineis:

busy. a

9. In a telephone exchange system, the

combination of a calling and called subscribers line, a jack associated with the called line, a cord circuit provided with a plug for engaging said jack, meansassociated with said cord circuit. for automatically indicating to the calling subscriber in case the called line is busy when the plug is placed in the jack, means associated with said cord circuit and rendered active in case the called line is not'busy for ringmg on said line, means controlled by the called subscriber upon answering to disable said ringing, additional means controlled by said subscriber for freeing his line'while the plug remains in the ack. Y

10 111 a telephone exchange system, the combination 0]. a plurality of groups of trunks the individual trunks of each group secondary trunk, said automatic selection being controlled over said calling line, a cord circuit associated with said secondary trunk, terminating in a calling plug, a ack associatedwith the called line, automatic means rendered operable aft/er theplug is inserted in the ack for testing the COIlClltion of the called line, means under control of a calling line for causingthe automatic disconnection of the calling line from the primary trunk and of the primary trunk from the secondary trunk, and means under control 01": the calling and called lines for freeing the called line from said cord 12. In a telephone exchange systennthe combination of a plurality of primary trunks, of a plurality of groups of secondary trunks for interconnecting with said primary trunks, a controlling relay individual to each of said groups of trunks, a switch common to all of said groups oi trunks, and means for operating said switch in case a particular group of trunks is busy, the operation of said switch serving to energize said relays in turn until a group of idle trunks is found for interconnection with said primary trunks. r

In testimony whereof I my signature in the presence of two witnesses.

JOSEPH L. WRIGHT.

Witnesses:

' H. PoLA'rsEK,

A. McCUNn. 

